Schottky diodes are widely used in switching power supplies, each person in the electronics industry have heard of the Schottky diode , but do we really understand the internal structure of the Schottky, applications and why Schottky widely used in high frequency switching power supply? So let us together into the Schottky world we want to find the answer.
There are various types of diodes: press material into the germanium diode, a silicon diode, a gallium arsenide diode; press die structure can be divided into point-contact diode and the surface contact diode; different uses can be divided into a rectifying diode, detector diode, zener diode, a varactor diode, a photodiode, a light emitting diode, a switching diode,
Fast recovery diode; it can be divided according to the type of junction semiconductor junction diode and metal-semiconductor junction diode, a Schottky diode but belongs to a metal-semiconductor junction diode.
First, the internal structure of the Schottky diode:
Schottky (Schottky) diode, also known as a Schottky barrier diode (referred to as the SBD), the diode is made of a metal barrier layer formed in contact with the semiconductor based made as shown below, and its main feature is the forward voltage drop of small (about 0.45V), a short reverse recovery times and small switching loss, is a low-power, ultra-high speed semiconductor device.
Schottky diodes in principle structurally very different from the PN junction diode, by its internal anode metal (molybdenum or the like with a barrier layer made of an aluminum material), silica (of SiO?) Electric field to eliminate materials, N - epitaxial layer (arsenic material), N-type silicon substrate, N + cathode layer and the cathode metal or the like,
As shown below. Schottky barrier is formed between the N-type substrate and the anode metal. When the Schottky barrier at both ends with a positive bias (anode metal positive power supply, N-type substrate connected to negative power supply), the Schottky barrier layer is narrowed, the internal resistance becomes small; on the contrary, if when both ends is reverse biased Schottky barrier, a Schottky barrier layer is wider, the internal resistance becomes large.
Second, the Schottky diode applications:
Switching power supply which we often use a Schottky diode , but due to different manufacturers vary greatly on performance and other reasons, the following parameters must be considered when we choose Schottky:
1, voltage drop VF
VF is the voltage drop across the diode when the diode forward, when the larger current through the diode, VF larger; when the diode temperature higher, the smaller the VF.
2, the reverse saturation leakage current IR
IR refers to addition of a reverse voltage across the diode, the current flowing through the diode, the Schottky diode reverse leakage current is large, the Schottky diode is selected to select a smaller IR diode.
3, rated current IF
Refers to a long-running diode, the current value according to the average temperature to allow conversion out.
4, the maximum surge current IFSM
Allowing excess forward current flows. It is not normal current, but the current moment, this value is quite large.
Third, the fast recovery diode Schottky comparison:
Fast recovery diode reverse recovery time is very short the diode (hereinafter 5us), the diode forward voltage drop than normal (0.8 ~ 2V) Reverse voltage 1200V or less, the performance can be divided into fast and ultrafast recovery recovery, which can reach 100ns or less.
Schottky diode reverse recovery time of 10ns or less, a large reverse leakage current, low voltage, typically below 150V are used for low voltage applications.
Schottky diodes and fast recovery diode differences: the former than the recovery time is about one hundred times smaller latter, the former reverse recovery time is about a few nanoseconds. The former has the advantage also low power consumption, high-current, ultra-high speed; the latter has a higher switching speed, can be obtained while a high voltage, a small reverse leakage, can be used for higher voltage and higher frequency applications .
Further Schottky diode ESD capacity less than fast recovery diode.